What New Mexico’s special election can tell us about the midterms

Analysis by Harry Enten, CNN

Tuesday’s special election to represent New Mexico’s 1st District in Congress is just one race. No matter who wins — likely the Democratic candidate Melanie Stansbury — control of Congress won’t change.

Yet, this race will also be one of our first insights into the political environment a little more than four months into President Joe Biden’s administration. Federal special elections, as a group, usually give us a fairly good idea how midterms are going to go.

Democrats barely won the House of Representatives in 2020. They took the national House popular vote by 3 points, leading to a small 5-seat majority. Any movement in the national environment toward the GOP is likely to result in the Democrats losing control of the chamber.

The key to understanding how to read Tuesday’s result in that context is that New Mexico’s 1st is a heavily Democratic district. President Joe Biden won it by 23 points last election. Hillary Clinton took it by 17 points in 2016. Democrat Deb Haaland, now the secretary of the Interior, won the district by 16 points in her 2020 re-election campaign.

It would take a truly unusual event for Republican Mark Moores to beat Stansbury. This heavily Democratic district covering much of Albuquerque just hasn’t voted for Republicans recently.

Democrats, though, don’t only want to win this election. They want to win it big because of what it says about the larger state of play.

Historically, the swing in House special elections from the last two presidential elections is telling. Combining the 2016 and 2020 results and giving more weight to the most recent one, New Mexico’s 1st District is about 18 points more Democratic than the nation as a whole.

This means that a basic baseline for Democrats is that Stansbury wins by 18 points. This isn’t an exact estimate, as other factors such as candidate quality can impact special elections, like any other election.

Still, the only other congressional special election this year turned out to be a heavily Republican affair. In Texas’ 6th District special election, the Republicans combined got 25 points more of the vote than the Democratic candidates. Biden had lost the district by a mere 3 points.

The Texas special election, though, was a jungle primary. All the candidates, regardless of party, ran against each other in one primary. There were more Republicans on the ballot, and the Republican candidates raised a lot more money.

In New Mexico, Democrats don’t have the same excuse. There is just one Democrat and one Republican on the ballot (along with some minor party candidates), and Democrats have spent a good amount of money on the race.

Democrats want Stansbury’s likely victory to at least come close to the +18 point Democratic baseline. Another clear underperformance, after Texas’ 6th, would be a true suggestion that the national environment has shifted since November.

Remember that we saw a lot of massive GOP underperformances in early 2017. Republican candidates from California to Kansas to Montana did considerably worse than former President Donald Trump did in those districts in 2016.

That foreshadowed trouble for Republicans in future special elections and the 2018 midterms. Democrats ended up outperforming the presidential result baseline by an average of 12 points in federal special elections between 2017 and 2018. They won the House popular vote by 9 points in the midterms, a small difference of 3 points.

From the 1994 to 2018 election cycles, the average swing in federal special elections from the previous presidential results has come within 3 points of the House popular vote in midterms. It’s not a perfect connection, but the correlation is high at +0.97.

In 2020, the federal special elections pointed to a much closer national environment than the polling that had Biden up by plenty. The special elections were closer to the truth.

The bottom line is Tuesday’s special election in New Mexico is a small piece of the puzzle. That said, history, especially recent history, indicates that it’s still an important piece.